1. Field of the Invention
The present invention relates to rack mount libraries for storage of electronic media such as data storage tapes and disks.
2. Background Art
Rack mount libraries are used to store electronic media so that the data stored on tape or disk is available. Data storage facilities periodically require expansion to accommodate additional media. Several approaches have been proposed to accommodate expansion. The simplest approach is to replace a smaller library with a larger library, but this is the most costly approach.
Another approach is to add an additional stand-alone library. This approach offers the advantage of simplicity because an additional stand-alone library is simple to install in a rack and can then be connected to a computer system. The problem with this approach is that it is expensive to add an additional library every time there is a need for added capacity. Costs are incurred each time an additional library is added for control electronics and a robotic system. Adding additional stand-alone libraries to expand capacity creates a management problem over time because certain systems may be limited to using particular libraries and tape drives. Extra tape drives may need to be purchased for each library so that spare drives are available in each library. A robot in one library normally cannot access tapes in another library.
The problem of making tapes or disks available in separate stand-alone libraries may be addressed by connecting the libraries together with a mechanism that allows tape cartridges or disks to be passed from one stand alone library to another. Control software modifications may be required to integrate two libraries into a single system. While this approach simplifies management of the two libraries, substantial costs are associated with providing each library with its own electronics and robotic system and the cost of the mechanism used to transfer tapes or disks from one library to another. Installation of the mechanism that moves the storage media between libraries requires trained service personnel to install and test the system. The mechanism that moves the media between libraries could potentially reduce the reliability of the overall system, especially if not properly installed.
A customer's needs for increased library storage capacity can also be addressed by having a customer purchase a larger library than needed at a reduced price with many of the cartridge locations being disabled until needed by a customer. The excess capacity in the library may be purchased at a later date by a customer when the need for more capacity arises. A customer may be required to pay to have the storage library upgraded to make added capacity available. It may be possible to upgrade software simply by entering a password. This approach saves the cost of duplicate electronics, transfer mechanisms, robotics and control systems that may be required if a second library is purchased. Problems with this approach are that the extra unused capacity takes up space in a rack that could be used for other equipment. In addition, since all of the components of the larger library are initially purchased, the cost of these components must be paid for up front with an additional charge being assessed only after there is a need to expand the available storage.
Expansion kits have been provided to address the problem of providing an economical, expandable library that can be added to an existing library. Examples of this type of system are the 2/20, 4/40, 6/60 and 6/140 library models sold by Hewlett Packard. A single vertical lift transport assembly can move through the entire library eliminating the need to provide a separate mechanism for moving cartridges between libraries. This approach also simplifies the requirements for control software and library management. This approach may also reduce the cost of storage library systems for the customer since the customer buys what they need when they need it. The problem with this approach is that adding a prior art expansion kit to a storage library is a relatively complicated process that requires substantial disassembly, removal and re-assembly. These systems have interface electronics boards in each expansion module that must be grounded to prevent damage to sensitive electronic components. The expansion kit must be accurately aligned and carefully assembled to be integrated into the system. Specially trained service personnel are required to install prior art expansion kits to ensure that the hardware is assembled properly. Unless expansion kits are installed by trained service personnel, the newly expanded library may be subject to operational problems. Using highly trained service personnel to assemble the components adds to the cost of providing an expandable library.
There is a need for a modular library that is expandable and may be expanded by a customer's own personnel. There is a need for a system that permits a customer to pay for only the storage library requirements that they need at the time of purchase and that allows them to order and install an expansion module themselves. Such an expansion module should be designed to be shipped directly to the customer who would be responsible for installing it into the rack with simple mechanical and electrical connectors. Finally, there is a need to provide such a system economically and without compromising system reliability.